Organic electroluminescent devices have features including selfluminous nature, wide angle of visibility, low-voltage drive, and high brightness and, in addition, a smaller number of layers necessary for constituting the device than liquid crystal devices, ease of production, realization of a thin device and the like. The organic electroluminescent devices having these features have drawn attention as display devices which are a successor to liquid crystal displays. In this connection, an important technical task involved in the preparation of color display devices using the organic electroluminescent device is to selectively form organic electroluminescent materials, which emit individual color lights, in a fine pattern.
At the present time, three methods are known for the preparation of a color display device using the organic electroluminescent device. The first method is to use a combination of a white light-emitting organic electroluminescent material with a color filter. The second method is a color conversion method which uses a blue light-emitting organic electroluminescent device and a color converting layer for converting the blue color of light emitted from the blue light-emitting organic electroluminescent device to red and/or green. The third method is to arrange an organic electroluminescent material capable of emitting red light, an organic electroluminescent material capable of emitting blue light, and an organic electroluminescent material capable of emitting green light separately from one another. Among the three methods, the third method can efficiently utilize the light emitted from the organic electroluminescent device, and the first and second methods suffer from a very low level of emitted light utilization which is about one-third of the total quality of luminescence.
The third method, however, is disadvantageous in that, since the organic electroluminescent materials are generally very low in resistance to a wet process, high definition cannot be realized by photolithography without difficulties. For this reason, in the third method, vapor deposition using a shadow mask is generally adopted for arranging the organic electroluminescent materials, which respectively emit red light, blue light, and green light, separately from one another. This method, however, involves many problems. For example, the fabrication of a shadow mask having a high density pattern is difficult. Further, when the fabrication of a shadow mask having a higher density pattern is desired, a thinner shadow mask should be used. In the case of a thin shadow mask, a vapor deposited film cannot be accurately formed without difficulties, for example, due to expansion/contraction-derived distortion of the shadow mask and sneak-in of vaporized material.
Regarding the third method, for example, Japanese Patent Laid-Open Nos. 011216/2000, 077182/2000, 307246/1999, 208881/1998, 054275/1999, and 167684/1997 disclose techniques wherein a transfer method is used in the preparation of a color display device. In the techniques disclosed in these publications, the transfer method used is basically a thermal dye sublimation transfer method wherein a luminescent material is sublimated and transferred. Thermal dye sublimation transfer requires a temperature high enough to sublimate the material used. Therefore, the support used should withstand the high temperature and, at the same time, should be suitable for transfer. However, it is difficult to find a support satisfying these requirements. Further, the formation of the luminescent material on a transfer medium is generally carried out by transfer. This poses a problem of productivity of the transfer medium. Further, an additional problem involved in the above method is that the sublimated material is disadvantageously scattered to parts where the sublimated material is not to be transferred. The technique disclosed in Japanese Patent Laid-Open No. 011216/2000 is disadvantageous in that the preparation of a transfer medium by forming convex protrusions on a high heat-conductive sheet and vapor depositing an organic material on the convex protrusions is troublesome. The technique disclosed in Japanese Patent Laid-Open No. 077182/2000 is also disadvantageous in that the preparation of a transfer medium is very difficult due to the structure of the transfer medium comprising a lattice- or band-shaped low heat-conductive part and a high heat-conductive part provided on its internal side. Thus, any satisfactory transfer method has not hitherto been developed.